The invention relates to control means for a bar feeder and holder coupled to a machine tool to hold bars for and feed bars to the machine tool and particularly to control means for a bar feeder and holder of the kind disclosed in our U.S.A. application Ser. No. 487,953 now U.S. Pat. No. 3,941,256, issued Mar. 2, 1976.
When feeding automatic machine tools with bar by means of a bar feeder, the problem arises that when a bar being machined is almost used up, a condition which must be avoided can arise wherein a remnant formed by the extreme tail-end of a bar is gripped only in the front end of the jaws of a collet and a length of the bar to form the workpiece projects from the collet into the machining space of a machine tool. If machining operations are attempted on a remnant of bar held in this way, the reaction of the remnant of bar to the cutting tool is likely to move the free end of the remnant away from the axis of rotation of the bar to cause it to sweep round in a circle, with consequent damage to the cutting tool and the jaws of the collet. To avoid the possibility of such a condition arising, it is normal practice to feed out of the collet and against a dead-stop a greater length of bar than is required to form a workpiece and then to traverse the dead-stop towards the collet before the collet is closed. Thus, it is ensured that there is always sufficient length of bar for safe machining, since if there is not sufficient bar the remnant of the bar will fall out of the collet before the movement of the dead-stop towards the collet begins. The disadvantage of this method is, however, that an unduy long time is required for each bar feed operation, the length of workpiece that can be machined is unduly restricted and an amount of space is required to permit the movement of the dead-stop such that there may not always be sufficient space to mount the maximum number of cutting tools which could otherwise be provided.